However, Scott McClellan said the administration was not planning to release any documents from Miers' service as White House counsel that might shed light on her experience with constitutional issues.

"She has deep knowledge of the Constitution and constitutional law," McClellan said at his daily briefing for reporters.

McClellan added that in her job, which Miers has held since early this year, she had to "deal on a daily basis" with matters such as the scope of presidential powers, the Constitution's commerce clause -- which gives the federal government a range of authority over the 50 states -- and executive privilege.

It is the doctrine of executive privilege that McClellan and other administration officials have cited in saying that documents relating to Miers' work at the White House is off-limits to the Senate Judiciary Committee, which will conduct her confirmation hearing.

McClellan said Friday that the release of such information "could have a chilling effect on the ability of the president to receive the kind of open and candid advice that he needs to protect the American people and carry out the other responsibilities that he has."

Before Miers became White House counsel, she served as a key aide to the president, and before that, as Bush's personal attorney. Bush's nomination of Miers has encountered unexpectedly strong opposition from Republicans as well as Democrats, many of whom contend that her work experience does not qualify her for the Supreme Court.

Citing questions about her background, the conservative National Review magazine called Friday for Miers to withdraw her nomination.

"Miers's own career as a lawyer shows a strong tendency to identify with local elites and establishments, to go along with prevailing ideas, and to avoid doing anything that might cause unpleasantness or rock the boat," the magazine's editors said in a posting on its website. "These are useful personality traits, but they are not the traits of a [Justice Antonin] Scalia or a [Justice Clarence] Thomas -- the kind of justice this president led conservatives to expect."

The editorial concluded: "The prudent course is for Miers to withdraw her own nomination in the interests of the president she loyally serves. The president could then start over."

Neither Miers nor the White House has given any sign that she would step aside.

Bush plans an event Monday in the Oval Office with three judges who will vouch for Miers' abilities. In a letter sent Friday to Senate Judiciary Chairman Arlen Specter (R-Pa.), the three former Texas Supreme Court justices -- Joe R. Greenhill, John L. Hill and Thomas R. Phillips -- praised Miers' "legal brilliance."

"Together we represent 34 years of experience on the Texas Supreme Court," the letter said. "We feel confident that we know what it takes to be a justice -- Harriet Miers exceeds that mark."

Bush's chief of staff, Andrew Card, acknowledged in a TV interview scheduled for broadcast Sunday on C-Span that White House officials were taken aback by the vehemence of opposition to Miers' nomination from some conservative quarters.

"I don't think they know her," Card said in the interview, which was taped Thursday. "I wish that they had been skeptical and looked to learn more about her and they would have been very comforted. I'm a little surprised that they came out of the box so cynically."

White House officials said Miers planned to spend the weekend answering a lengthy questionnaire about her background and experience for the Senate Judiciary Committee.

On Monday, she is scheduled to meet with Sens. Dianne Feinstein (D-Calif.) and Charles E. Schumer (D-N.Y.), both members of the judiciary committee, and to have a second meeting with Specter.